1. Field of the Invention
The present invention pertains generally to flexible tubular inner members of angled rotary tissue cutting instruments and, more particularly, to flexible tubular inner members having flexible couplings for transmitting torque to rotate a cutting element at the distal end of the inner member in an angled rotary tissue cutting instrument.
2. Brief Discussion of the Related Art
Rotary tissue cutting instruments have become well accepted for use in cutting anatomical tissue at surgical sites in many various surgical procedures, especially those in which access to the surgical site is gained through a relatively narrow or small size natural or artificially created passage. Rotary tissue cutting instruments are typically characterized by an elongate tubular outer member having a distal end with an opening therein defining a cutting port or window for receiving anatomical tissue, and by an elongate tubular inner member that has a distal cutting element positioned for rotation past the cutting window. The tubular inner member is rotatably disposed within the tubular outer member to rotate the cutting element to cut the anatomical tissue received in the cutting window. Proximal ends of the outer and inner members are normally attached to hubs that are engageable with a powered surgical handpiece having a motor that rotates the inner member relative to and within the outer member. The cutting window of the outer member and the cutting element of the inner member can each have various configurations. The outer member cutting window can be provided with a cutting edge or formation that cooperates with a cutting edge or formation of the inner member cutting element to cut the anatomical tissue.
Rotary tissue cutting instruments in which the outer member is longitudinally or axially straight are unsuitable for accessing some surgical sites. It has therefore been recognized to provide angled rotary tissue cutting instruments in which the tubular outer member is longitudinally bent, angled or curved in order to facilitate positioning of the distal end of the instrument at the surgical site as represented by U.S. Pat. No. 4,646,738 to Trott, U.S. Pat. No. 6,312,438 B1 to Adams, U.S. Pat. No. 6,533,749 B1 to Mitusina et al and U.S. Pat. No. 6,656,195 B2 to Peters et al. In angled rotary tissue cutting instruments, the inner member normally has a flexible region disposed within the bend, angle or curve of the outer member that transmits torque to rotate the cutting element while conforming to the bent, angled or curved configuration of the outer member.
Various designs have been proposed for the flexible regions used in the inner members of angled rotary tissue cutting instruments, including designs involving multiple spirals. The aforementioned Trott patent describes a flexible transmission interconnecting a distal end portion and a proximal end portion of the tubular inner member of a rotary surgical tool, where the flexible transmission is composed of three spirals, i.e. an inner spiral, a middle spiral and an outer spiral, alternately wound in opposite directions and spot-welded together at opposite ends. The spirals are made from flat stainless steel ribbons which are apparently the same width for each spiral as well as being the same thickness for each spiral. The rotary surgical tool disclosed in the Trott patent was marketed under the name of “Merlin” and was limited to operation with the outer member bent to a maximum of only about a 15 degree angle. Furthermore, it was found that the spirals of the flexible transmission could undesirably stretch prior to assembly of the inner member with the outer member. In practice, an inner member in which the flexible transmission had undesirably stretched would be discarded and not used, thereby necessitating a replacement inner member and resulting in increased cost.
The aforementioned Adams, Mitusina et al and Peters et al patents disclose tubular inner members of angled rotary tissue cutting instruments that have flexible regions composed of a helical or spiral cut formed in the body of an inner tube, and inner and outer spiral wraps disposed over the helically cut region of the inner tube. Flat strips of material are used to form the inner and outer spiral wraps, the strips apparently being the same width for both the inner and outer spiral wraps and apparently being the same thickness for both the inner and outer spiral wraps.
U.S. Pat. No. 6,053,922 to Krause et al discloses a flexible shaft for transmitting rotary power from a driven end to a driven part along a non-straight path, particularly the medullary canal of the femur. The flexible shaft is characterized by a helical or spiral slot cut in a tube in a pattern defining interlocked adjacent tube segments, without any spiral wrap being disposed over the slotted region of the tube.
U.S. Pat. No. 6,344,037 B1 to Suorsa et al pertains to an integrated coaxial transmission line and flexible drive cable for use in catheter systems and including inner wound and outer wound wires disposed over a core. The inner and outer wound wires have a round cross-section as opposed to a rectangular cross-section as found in a flat strip of material.